The present invention relates to a wire rope. More particularly to a wire rope comprising a plurality of wires, the wire rope having stranded construction, and the wire rope being subjected to suitable treatment such as swaging.
Generally, in the normal driving condition a seat belt used for an automobile is provided in such a manner that a person seated on the automobile seat is loosely tied by the seat belt. But in the moment of collision, tension is applied to the seat belt in such a manner that in the automobile the person is firmly tied by the seat belt. As a means for operating the seat belt in the emergency, wire rope is generally used. However, there are so many ropes having sufficient flexibility, but lacking tensile strength. This is because the diameter of each wire is reduced in order to increase flexibility.
However, when diameter of each wire is reduced, the gap or space between two adjacent wires of the wires constituting a wire rope increases even if number of the wires is increased. For that reason, the strength of each of the wires per unit area is decreased. Therefore, in the stranded ropes having a predetermined diameter in which both high strength and high flexibility are required, either strength or flexibility is sacrificed.
In Japanese Unexamined Patent Publication No. 508193/1995, as shown in FIG. 6, there is described a stranded wire rope having a construction of 19.times.7, the stranded wire rope being subjected to swaging so that a wire gap ratio can be 22% which is defined as: EQU wire gap ratio=(1-(S/A)).times.100 (%)
wherein
S: summation of sectional areas of each of the wires constituting the stranded wire rope before subjecting to swaging, and
A: area of circumscribed circle of the wire rope after subjecting the wire rope to swaging.
However, in this wire rope mean wire diameter ratio is about 6.5% which is defined as: EQU mean wire diameter ratio=(d/D).times.100 (%)
wherein
d: mean diameter of each wire before subjecting to swaging, and
D: diameter of the wire rope before subjecting the wire to swaging.
Therefore, in this wire rope, flexibility is not preferable, and this wire rope cannot be practically used as a wire rope for operating a seat belt.
Further, in Japanese Unexamined Patent Publication No. 508193/1995, as shown in FIG. 8, there is described a stranded wire rope having a construction of 19.times.19, the stranded wire rope being subjected to swaging so that a wire gap ratio can be 12%. However, in this wire rope, distortion due to swaging treatment becomes remarkable. As a result, the strength of the wire rope after subjecting the wire rope to swaging is smaller than that before subjecting the wire rope to swaging. Flexibility is also reduced due to interference of wires. Therefore, this wire rope cannot be used as a wire rope for operating a seat belt.
Furthermore, in Japanese Unexamined Patent Publication No. 508193/1995, as shown in FIG. 7, there is described a stranded wire rope having a construction of 7.times.7.times.7, the stranded wire rope being subjected to swaging so that a wire gap ratio can be 36%. However, in this wire rope, wire gap ratio is more than 35%. For that reason, the wire rope having a predetermined diameter cannot satisfy the required strength.
Therefore, this wire rope cannot be used as a wire rope for operating a seat belt.